1. Field of the Invention
This invention relates to a packaging process and structure of an electronic device, and more particularly to a packaging process and structure of an electronic device of an IC (integrated circuit) chip.
2. Description of Related Art
In IC industry, IC package is used for providing the chip with a medium of electrical connection to a PCB (printed circuit board) or to other appropriate devices. In addition, the package also provides the chip a protection from being damaged or short-circuit. And the packaging process is the last process in making the IC products. The IC circuit is generally encapsulated in a package and is then bonded to the PCB or other substrates.
During the packaging process, a two-piece molding equipment is normally employed and a molding compound is generally used to perform encapsulating process for the electronic devices such as IC chip. A chip-carrying substrate is placed into the cavity of a mold, then the molding compound is introduced into the cavity through the mold runner of the mold to encapsulate the chip, afterward, the mold is separated from the package after the molding compound is cured. At this moment, however, since the package is still connected to the molding compound that is cured and is positioned in the mold runner, a degating process is then performed to remove the excess portion so as to accomplish the fabrication of an electronic package.
However, since there are bonding forces existed between the substrate and the molding compound that is positioned in the mold runner, while performing the degating process to remove the excess portion of the molding compound, the substrate will be twisted. In turn, the solder mask on the substrate is impaired, the conductive trace is cracked, and delamination occurs between the molding compound, solder mask, conductive trace, chip, and the substrate, consequently, gaps are generated. Subsequently, moisture penetrates into the gaps which results in the moisture expansion due to the heat to generate the "Popcorn Effect" that eventually damages the package.
Shown in FIG. 1 is a top view of a package substrate according to the prior art presented in 1994 by Amkor Company and Anam Company with U.S. Pat. No. 5,635,671. A Degating Region 102 made of Gold (Au) or Palladium (Pd) is formed on the mold runner 104 of the substrate. The width of the Degating Region 102 is greater 15 than that of the mold runner 104. Since the bondability of the molding compound to the gold Degating Region 102 is smaller than the bondability of the molding compound to the substrate 100, the package structure will not be damaged when it comes to removing the excess molding compound in the mold runner. But the gold Degating Region 102 occupies the substrate area available for the circuit pattern, besides, the fabrication of the gold Degating Region 102 will increase the manufacturing cost of the package.
Shown in FIG. 2 is an isometric view of a schematic drawing showing the process of removing the excess molding compound according to the prior art presented in 1991 by Motorola Company with U.S. Pat. No. 5,542,171. As shown in the FIG. 2, a sputter etching process is performed to a substrate 200 in order to enhance the bondability between the molding compound and the substrate in the subsequent process. Then a contamination process is performed that a coating layer 206 of permanent marking ink or polymer is applied on the contact area between the substrate 200 and a gate 204 through which the mold runner 210 is connected to the semiconductor chip 202. The coating layer 206 is applied for reducing the bondability between the molding compound and the substrate such that the package structure will not be damaged when it comes to removing the excess molding compound in the mold runner. But the above-mentioned coating process by using the permanent marking ink or polymer is complicated and difficult. The method not only increases the manufacturing cost but also has the concern of damaging the quality of the products.